The present invention relates to rocker arm assemblies for internal combustion engines and, in particular, to rocker arm assemblies with an improved mechanism for engaging a valve stem.
Rocker arm assemblies are utilized in internal combustion engines for alternately actuating intake and exhaust valves. As an engine cam shaft rotates, a push rod is selectively actuated by cams located on the cam shaft. The push rods, in turn, direct an upward force on one end of a rocker arm to cause the rocker arm to pivot about a pivot point. As the rocker arm pivots, its opposite end generates a downward force to selectively open an engine valve. Thus, the rocker arm translates the motion of the cam shaft into the opening of the engine valves. Since the timing of the opening of the intake and exhaust valves is important to proper operation of an internal combustion engine, anything that interferes with the timing will detrimentally effect engine performance.
Typically, known rocker arms are integral, one-piece components having a first end, a,second end, and an intermediate portion for pivotally mounting the rocker arm. The first end of the rocker arm has a push rod engagement portion that engages with an upper end of a push rod. Typically, the push rod engagement portion is a downwardly facing recess which receives the upper end of the push rod. The second end of the rocker arm includes a contact surface that engages a valve stem. One known rocker arm uses a downwardly facing pad as a contact surface. Another known rocker arm uses a roller member positioned in a recess formed in the second end of the rocker arm as a contact surface.
However, prior art designs for engaging the valve stems are undesirable in that they are susceptible to scrubbing. Scrubbing is abrasion of the rocker arm and the valve stem due to friction. Scrubbing leads to unwanted physical deterioration of the rocker arm and the valve stem, which in turn leads to irregularity in the timing relationship between the cam shaft and the valves. Irregularity in the timing relationship increases engine noise and decreased engine operation efficiency.
Accordingly, there is a need to provide an improved, cost-effective rocker arm that minimizes or eliminates scrubbing, thereby prolonging operational life of the rocker arm and valve stem.
The present invention is directed to a rocker arm having a first end, a second end, and an intermediate portion. A pivoting clevis is pivotally mounted to the second end of the rocker arm for engaging a valve stem or a bridge that activates dual valves. The clevis has a flat contacting surface facing downward and an internal recess formed by two upwardly extending walls and an upwardly facing cam surface for receiving the second end of the rocker arm. A downwardly extending portion of the second end mates with the upwardly facing engagement surface of the clevis.
The clevis is attached to the second end of the rocker arm by an attachment pin that extends through the upwardly extending walls of the clevis and through the second end of the rocker arm such that the clevis selectively pivots about the attachment pin. The downwardly extending portion of the second end and the upwardly facing cam surface of the clevis maintain sliding contact throughout the motion of the rocker arm to provide pivoting action of the clevis. The pivot action of the clevis minimizes or eliminate scrubbing while maintaining contact with the valve stem or bridge.